visual-diff-mode

Use color-coding to compare two buffers.

The visual-diff command creates a buffer in visual diff mode that
shows the changes between one buffer and another. Added lines are
shown with a yellow background, deleted lines are shown with a red
background, and common lines are colored as in the original buffers.

In a visual-diff buffer, the keys Alt-<Down> and Alt-] move to the
start of the next changed or common section. The keys Alt-<Up> and
Alt-[ move to the previous one.